Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 300146

Area Forecast Discussion
National Weather Service Lincoln IL
846 PM CDT MON AUG 29 2016

Issued at 835 PM CDT Mon Aug 29 2016

Weak stationary frontal boundary over northeast Illinois early
this evening was once again the focus for widespread showers
and storms, which extended west into central through eastern
Iowa today. Further south, much less coverage was noted with
very little focus for storms to develop this afternoon and
early evening. The convection has dissipated across our area
but in this moist environment, can`t entirely rule out a stray
storm overnight, especially along and west of the Interstate
55 corridor where we will continue to carry low chance POPs
for the early morning hours. With the abundant low level
moisture in place, nearly calm winds and mainly just cirrus
clouds to deal with overnight, we could see some patchy fog
develop again, especially in areas that received some rain
this afternoon. We should have the update out by 900 pm.


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 248 PM CDT Mon Aug 29 2016

19z/2pm water vapor imagery shows upper high centered over southwest
Indiana...with fetch of deep moisture flowing around the high from
the Gulf of Mexico N/NW into Missouri/Iowa and western Illinois.
Scattered diurnal thunderstorms have developed within the moisture
plume, primarily along/west of the I-55 corridor.  As has been the
case over the past few days, steering currents aloft are quite weak
and the storms are very slow-moving.  As a result, heavy rainfall
and localized flash flooding will be possible across the western
half of the KILX CWA through the afternoon into the early evening.
Once the sun sets and instability wanes, the storms will gradually
dissipate by mid to late evening.  Have therefore included chance
PoPs everywhere along/west of I-55 this evening...dropping down to
just slight chance overnight.

Rain chances will become more focused during the day Tuesday as a
cold front currently over the Northern Plains approaches from the
west.  Have therefore increased PoPs to high chance across all but
the far E/SE CWA.  Given precipitable water values of 2 to 2.5, any
storms that develop will once again be capable of producing
torrential downpours and localized flash flooding.  High
temperatures will range from the lower 80s northwest of the
Illinois around 90 degrees south of I-70.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 248 PM CDT Mon Aug 29 2016

A weak slow moving upper level trough will be moving through the
Midwest Tuesday evening promoting scattered showers and
thunderstorms across especially northwestern portions of the central
and southeast IL forecast area through the night. With weak sfc-6km
shear values less than 20 kts and widespread cloud cover, severe
thunderstorm risk is minimal. Localized heavy rainfall will be a
risk as storm motion should remain very slow along with a slow moving
upper feature.

For Wednesday...Models have continued a trend of deepening a trough
farther westward into the Midwest and pushing a substantial cold
front southward through the region including central IL. Initially,
this will bring another focus for scattered thunderstorms. Although
timing differences continue, the consensus of 12Z models today bring
the associated rainfall to an end during the afternoon in the
northern parts of the forecast area north of I-74, while areas to
the south should see an end to precipitation by evening. Wednesday
south of I-70. A downtrend in temperature will begin Wednesday
starting with lows Wednesday morning upper 60s to around 70 in the
warm, humid, and cloudy air mass ahead of the front...followed by
highs ranging from around 80 along I-74 to as high as 85 south of
I-70. Lows Wednesday night should drop into the upper 50s to lower
60s as dewpoints drop into the 50s, down from the humid 70s prior to
the frontal passage.

Thursday through the weekend...dry conditions can be expected as the
cool and dry air mass slowly moderates through the period and high
pressure develops over the Great Lakes Region. Expect highs in the
upper 70s Thursday gradually rising to the mid 80s by Monday.
Dewpoints should be in the 50s to lower 60s through Saturday,
increasing to the 60s to around 70 by Monday.

As troughing slowly works its way eastward into the central U.S.
and a frontal zone develops in the Plains...chances for
precipitation look to start again northwest of the Illinois River on
Labor Day.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 545 PM CDT Mon Aug 29 2016

Mainly VFR conditions are expected this forecast period outside
any TSRA, which are expected to isolated. Once again, like it has
been the past several mornings, there may be a period of MVFR cigs
and vsbys in some shallow ground fog, but that should not persist
very long, if it develops at all. Most of the showers and storms
will dissipate by 02z this evening leaving a partly cloudy sky
overnight. Can`t rule out an isolated storm again during the early
morning hours, but coverage looks to be too limited to even
include a VCTS at this time. Once any fog/MVFR cig lifts Tuesday
morning, we are expecting scattered to occasionally bkn cumulus to
develop after 17z with cig bases in the 2500-3500 foot range
initially, which should then lift to between 3500-4500 feet by
afternoon. Surface winds will again be on the light side this
period with speeds generally running from 5 kts or less mainly
from an east to southeast direction.


.ILX Watches/Warnings/Advisories...


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